<!DOCTYPE html>
<html>
<head lang="en">
  <meta charset="UTF-8">
  <title></title>
  <style>
    * {
      margin: 0;
      padding: 0;
    }

    table {
      border-collapse: collapse;
      border-spacing: 0;
      border: 1px solid #c0c0c0;
      width: 500px;
      margin: 100px auto;
      text-align: center;
    }

    th {
      background-color: #09c;
      font: bold 16px "微软雅黑";
      color: #fff;
      height: 24px;
    }

    td {
      border: 1px solid #d0d0d0;
      color: #404060;
      padding: 10px;
    }

    .allCheck {
      width: 80px;
    }
  </style>
</head>

<body>
<table>
  <tr>
    <th class="allCheck">
      <input type="checkbox" name="" id="checkAll"> <span class="all">全选</span>
    </th>
    <th>商品</th>
    <th>商家</th>
    <th>价格</th>
  </tr>
  <tr>
    <td>
      <input type="checkbox" name="check" class="ck">
    </td>
    <td>小米手机</td>
    <td>小米</td>
    <td>￥1999</td>
  </tr>
  <tr>
    <td>
      <input type="checkbox" name="check" class="ck">
    </td>
    <td>小米净水器</td>
    <td>小米</td>
    <td>￥4999</td>
  </tr>
  <tr>
    <td>
      <input type="checkbox" name="check" class="ck">
    </td>
    <td>小米电视</td>
    <td>小米</td>
    <td>￥5999</td>
  </tr>
</table>
<script>
    const checkAll=document.querySelector('#checkAll')
    const cks=document.querySelectorAll('.ck')
    checkAll.addEventListener('click',function (){
      for (let i=0;i<cks.length;i++){
        cks[i].checked=this.checked
      }
    })
    for (let i=0;i<cks.length;i++){
      cks[i].addEventListener('click',function (){
        if (document.querySelectorAll('.ck:checked').length===3){
          checkAll.checked=true
        }
      })
    }
</script>
</body>
</html>